NSSS4.2

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4.2 How Minerals Form

Vocabulary

Solution: A mixture in which a substance dissolves in another substance.
Vein: A narrow channel of a mineral that is very different from the surrounding rock.

Outline

Introduction

  • Have you ever been to Crater National Park in Arkansas?
    • If you haven't, it is a park where you can search for diamonds.
      • So far, visitors have found more than 20,000 diamonds.

Processes That Form Minerals

  • Minerals can be formed by,
    • Crystallization of melted material
    • Crystallization of dissolved mineral

Minerals From Magma

  • When hot magma cools inside of the crust or when lava cools on the surface of the crust, minerals form
    • When they cool, they form crystals
    • The size of these crystals depends on
      • The cooling rate of the magma.
      • The amount of gas which the magma contains
      • The chemical composition of the magma
  • When magma deep below the surface cools slowly, over thousands of years, large crystals form
  • Magma closer to the surface cools faster then magma deep below the surface
    • Because of this rapid cooling, the crystals have less time to form thus being smaller

Minerals From Hot Water Solutions

  • When minerals dissolved in water ( which has been heated by magma ) cool, the elements and compounds leave the solution and crystallize as minerals.
  • When pure metals crystallize underground, they form veins
    • Veins form when solutions of hot water and metals follow cracks underground and crystallize.
  • Solutions usually form where tectonic plates spread apart along the mid-ocean ridge
    • First, water from the ocean seeps through cracks in the crust
      • Then, the water comes in contact with magma which heats it to a very high temperature.
        • After that, the heated water dissolves minerals in the crust and billows out of vents
          • Finally, the solution hits the cold sea and the minerals crystallize, sinking to the ocean floor.Ronaldo_soccer1jpg.jpg

Minerals Formed by Evaporation

  • When solutions evaporate, minerals can form
    • Deposits of the mineral halite have been formed the same way over millions of years

Where Minerals Are Found

  • Common minerals are spread evenly around the crust
  • Rarer and more valuable minerals are spread unevenly around the crust
  • Many valuable minerals are found near volcanic activity and mountain building

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